i just got a bigger exhaust on my 99 civic with a td04-15G turbo. Before i had a greddy PE exhaust and was able to boost 13psi easy. Now with the new bigger exhaust i can't boost more then 8psi. I called greddy and they said that too much flow can hurt performance. I don't think thats true. I have a blitz dsbc boost controller and i turned it all the way up but no use.

 

Are you running something like a 5 1/2" exhaust now or something? Greddy is right. What it sounds like to me is a boost controller line has gotten disconnected and the turbo is running off of your wastegate to regulate boost. Check your lines and go from there.